harfbuzz-sys: Use dep syntax.

[waywardmonkeys]

This prevents creating implicit features for core-graphics, core-text, foreign-types, freetype-sys, and windows.

Before:

❯ cargo add harfbuzz-sys
    Updating crates.io index
      Adding harfbuzz-sys v0.6.1 to dependencies
             Features:
             + core-graphics
             + core-text
             + coretext
             + directwrite
             + foreign-types
             + freetype
             + freetype-sys
             + winapi
             - bundled
    Updating crates.io index

After:

❯ cargo add harfbuzz-sys --path ../rust-harfbuzz/harfbuzz-sys
      Adding harfbuzz-sys (local) to dependencies
             Features:
             + coretext
             + directwrite
             + freetype
             - bundled
    Updating crates.io index